There is a requirement to provide control circuits for an aircraft with lightning strike protection circuits in order to avoid damage to the control circuits in the event of the aircraft being struck by lightning. In a known electronic assembly, the lightning strike protection circuits are provided on circuit boards or cards which are mounted upon and electrically connected to a motherboard in the usual manner. It is desirable to be able to test the operation of the lightning strike protection circuits as, in normal use, these circuits are effectively dormant and so any faults could remain unnoticed for a long period of time. However, testing of the lightning strike protection circuits of the type described hereinbefore requires removal of the circuit boards or cards carrying the circuits from the motherboard, and this may require disassembly of a substantial portion of the assembly, thus testing is a relatively complex and time consuming operation.